Air bleed press with hot gas drying



Oct. 6, 1959 HQRNBQSTEL ET AL 2,907,690

AIR BLEED PRESS WITH HOT GAS DRYING Filed Feb. s. 1958 [hf E27 [0P5 L/oyd Horn bosfe/ [award 0. lamb/e Z7 57 W, y w fl/fg s.

2,907,690 AIR BLEED PRESS wrrn nor GAS DRYING Lloyd Hornbostel and Edward D. Beachler, Beloit, Wis., assignors to Beloit Iron Works, Beloit, Wis., a corporation of Wisconsin Application February 6, 1958, Serial No. 713,669 Claims. or. 162-406) The instant invention relates to a press with an associated hot gas drying device, and more particularly, to

drying device.

Although 'the instant invention may have use in a number of fields involving the drying of paper, fabrics or the like in a press, the instant invention is particularly useful in the art of paper making and will be described primarily in connection therewith. As is known, paper machine presses comprise a pair of press rolls in a nipdefining relation which receive the paper to be dewatered at the nip. Such dewatering is accomplished by the combination of pressure applied to the web and suction applied through the shells of one or both of the rolls to remove water pressed out of the web. In suction presses, the suction roll is formed with a perforate shell and a felt is ordinarily trained over the perforate shell to protect the web against actual contact with such perforate shell. The vacuum within the suction roll must thus act through the felt to effect dewatering. With greater paper machine speeds, it will be appreciated that there are practical limitations to the amount of vacuum which can be created Withinthe suction roll and practical limitations as. to the water permeability of felts which are used in the presses. Also, the amount of pressure actually applied to the web at the press nip has practical limitations. The greater the rate of operating speed of the papermac'hine, the greater the tendency for water to buildup at the incoming side of the press nip.

Theinstant invention affords means and method for greatly increasing the dewatering effect at apress nip. In the instant invention the felt is preferably maintained separate from the web at the approach of the press nip, so that the pressure differential across the felt created by the suction .area of the suction roll may act most effectively; and hot gas means are mounted in close running relation to the nip so as to aim hot gas at the felt in this region. The hot gas serves to increase the temperature of the water building up' at the back side of the nip and the water present in the felt. This results in a, substantial decrease in the viscosity of the water and permits the waterlto flow through the felt much more freely.

The instant invention resides in a method and apparatus for effecting an increase in temperature of the felt and the Water carried thereby. This assists in replacing the heat of vaporization of the water which is evaporated due to suction in the suction roll. This also results in a reduction in the total weight of air handled in the suction roll and in a reduction in the power required by pump means to maintain vacuum in the suction roll. The hot gas or hot air materially reduces the viscosity of the water, so that the effective water permeability of the felt is increased. Also, the hot dry gas flowing at the nip tends to dry the surface of the felt and thereby to increase the rate at which the felt can absorb water.

It is, therefore, an important object of the instant invention to provide an improved method and apparatus an air bleed press in a paper machine having a hot gas for the operation of a high speed press in a paper machine, using hot gas drying.

Another object of the instant invention resides in the provision of an improved paper machine press section comprising a pair of press rolls defining a press nip receiving a web, one of said rolls being a suction roll, a felt lapping the suction roll and traveling through said nip, and hot gas means mounted inclose running relation to said nip aiming hot gas at the felt.

Still another object of the instant invention involves the provision of an improved method of dewatering a web that comprises conveying the web on a traveling felt, subjecting the web and felt to pressure along a line transverse to the direction of travel thereof to squeeze water therefrom, creating a pressure differential across thefelt to draw water therefrom in the region of said line, and subjecting the felt to a hot gas blast in the region of said line to heat the water there present and reduce the viscosity thereof.

Other and further objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed disclosure thereof and the drawings attached hereto and made a part hereof. a

On the drawings:

Figure 1 is an essentially diagrammatic elevational view showing a press embodying the instant invention; and

Figure 2 is a fragmentary detail view of the press nip of Figure 1, shown in elevation.

As shown on the drawings:

In Figure 1, there is shown a press, as indicated generally by the reference numeral 10 formed by a pair" of press rolls 11 and 12 defining therebetween a nip N which receives a paper web W traveling in the direction indicated by the arrowhead. One of the rolls 11 is a suction'roll having the conventional perforate shell and a suction gland 11a defining a suction area A straddling the nip N. A looped felt 13 (shown incompletely on guide rolls 14 and 15) laps the suotionroll 11 and travels through the nip N. The felt 13 covers: completely the suction area A, and the web W is guided by the bare roll 12 and guide rolls 16 and 17 so that the felt 13.is uncovered by the web W for most of its run over the suction area A on both the oncoming and off-running sides of the nip N.

At the oncoming side of the nip N there is mounted a hot air or hot gas flow means or nozzle 18 which aims hot gas at the felt 13 at the nip N. The nozzle 18 is mounted in close running relation to the nip N and is aimed generally at the nip N and at the felt 13 covering the suction area A in the immediate vicinity of the nip N.

As is indicated diagrammatically a pump P evacuates the suction roll 11 through a vacuum line 19 so as to maintain the desired amount of vacuum within the suction roll 11 (and applied at the suction area A)., The vacuum line 19 feeds through a water trap to remove entrained water at T into the suction side of thepump P. The pump P effects adiabatic compression of the air from the vacuum line 19 so as to increase the temperature thereof. Preferably, a heat exchanger H (for heating the air with steam) or similar heating device is mounted at the discharge of the pump P and heats the air discharged from the pump P to a temperature within the range of 500 to 1200 F. The resulting hot gas or air is fed through a hot gas line 20 into the nozzle 18. The advantage of this arrangement is that adiabatic compression of the air through the suction pump P effects some if not all of the necessary heating thereof, so that the hot gas is generated in a most efiicient manner.

The air which normally surrounds a press nip has a temperature of 70 to F. and has a relative humidity of quite close to 100%, because of the excessive amount of moisture present. The instant invention results in heating the air surrounding the nip to a substantially higher temperature thus materially decreasing its relative humidity and increasing its ability to absorb moisture. The exact temperature to which the felt 13 is heated will depend to some extent upon the felt characteristics, but the temperature of the hot gas should be within the range of 500 to 1200 F. This results in an addition of heat to the system compensating for the heat loss in vaporization of moisture at the suction area A. It will also be appreciated that the volume of hot air thus entering into the suction area is capable of absorption of greater. amounts of moisture and this hot air weighs substantially less than a corresponding volume of cool air or air at room temperature. This reduces the total weight of air handled by the pump P and reduces the power requirement for the pump P.

Referring to the details of Figure 2, it will be seen that the nozzle 18 is provided with apertures 18a and 18b through which the hot air flows. The Web W is retained on the surface of the bare roll 12 at the nip N and the web remains attached to the bare roll surface 12 at the off-running side of the nip N. The felt 13 covers completely the suction area A defined by an oncoming sealing strip 21 and an olf-running sealing strip 22. Within the suction area A there is a small land area a1 whereat actual nip pressure is applied to the web W and the felt 13. There is a substantial (angular) area a-2 at the oncoming side of the suction area, from the oncoming sealing strip 21 to the land area a1. In the oncoming area a-2 the felt 13 is uncovered by the web W; and it will be noted that this oncoming area 11-2 is substantially greater than the land or nip area a-l. The off-running area a-3 between the land area a-1 and the off-running sealing strip 22 is likewise substantially greater than the land area -1 and the felt 13 is, likewise, uncovered by the Web W in the off-running area a-3.

It will be noted that the nozzle 18 extends to opposite the oncoming area a-2 and is aimed at the felt 13 in this region of the oncoming area a2. In this region the vacuum of the suction area A draws moisture from the felt 13 and opens up the pores of the felt 13 just prior to the application of nip pressure. The heating of the felt 13 reduces the viscosity of the moisture therein and greatly accelerates the removal of such moisture into the suction area. In addition, the heating of the felt 13 in the region of the oncoming area a-2 tends to dry at least the surface of the felt 13 so that its ability to absorb water at the nip N is greatly increased. In addition, the elevated temperature of the felt 13 and the moisture retained therein elfects a corresponding increase in the temperature of the water at the land area a-l of the nip N, so that all of the water at the nip N is heated and its viscosity is correspondingly decreased. This decrease in viscosity greatly accelerates the physical withdrawal of water from the nip N through the felt 13 and the perforated shell 11b of the suction roll 11.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.

I claim as my invention:

1. In a paper machine press section, a pair of press rolls defining a press nip receiving a web, one of said rolls being a suction roll, a suction gland in said suction roll defining a suction area at the nip straddling the nip, a felt lapping the suction roll and traveling through said nip with the felt being uncovered by the web for most of its run over the suction area on both the oncoming and offrunning sides of the nip, and hot gas means mounted in closerunning relation to said nip aiming hot gas at the uncovered felt at the oncoming side of the nip.

2. In a paper machine press section, a pair of press rolls defining a press nip receiving a web, one of said rolls being a suction roll with a suction area straddling the nip, a felt lapping the suction roll and traveling through said nip with the felt'being uncovered by the web for most of its run over the suction area on both the oncoming and off-running sides of the nip, hot gas means mounted in close running relation to said nip aiming hot gas at the uncovered felt at the oncoming side of. the nip, and pump means evacuating said suction roll and discharging into said hot gas means.

3. In a paper machine press section, a pair of press rolls-defining a press nip receiving a web, one of said rolls being a suction roll, a felt lapping the suction roll and traveling through said nip, and hot gas means mounted in close running relation to said nip aiming hot gas between the .felt and the web at the oncoming side of said 1. In a paper machine press section, a pair of press rolls defining a press nip receiving a Web, one of said rolls being a suction roll, a suction gland in said suction roll defining a suction area at the nip, a felt lapping the suction roll and traveling through said nip, said felt being uncovered by the web foremost of its run over the suction area at the oncoming side of the nip,.and gas blast means mounted in close running relation to said nip aiming gas at the uncovered felt portion covering the suction area.

5. A method of dewatering a web that comprises conveying the web' on a traveling felt, subjecting the web and felt to pressurealong a line transverse to the direction of travel thereof to squeeze water therefrom, creating a pressure differential across the felt to draw water therefrom in the region of said line, maintaining the web and felt separate just ahead of said line, and subjecting the uncovered felt'just ahead of said line to a hot gas blast in the region of said line to heat the water present and reduce the-viscosity thereof.

7 References Cited in the file ofthis patent UNITED STATES PATENTS 689,400 Keeney Dec. 24, 1901 992,688 Pope May 16, 1911 1,140,711 Pope May 25, 1915 1,549,338 Tompkins Aug. 11, 1925 1,898,611 Berry et a1 Feb. 21,1933 

1. IN A PAPER MACHINE PRESS SECTION, A PAIR OF PRESS ROLLS DEFINING A PRESS NIP RECEIVING A WEB, ONE OF SAID ROLLS BEING A SUCTION ROLL, A SUCTION GLAND IN SAID SUCTION ROLL DEFINING A SUCTION AREA AT THE NIP STRADDLING THE NIP, A FELT LAPPING THE SUCTION ROLL AND TRAVELING THROUGH SAID NIP WITH THE FELT BEING UNCOVERED BY THE WEB FOR MOST OF ITS RUN OVER THE SUCTION AREA ON BOTH THE ONCOMING AND OFFRUNNING SIDES OF THE NIP, AND HOT GAS MEANS MOUNTED IN CLOSE RUNNING RELATION TO SAID NIP AIMING HOT GAS AT THE UNCOVERED FELT AT THE ONCOMING SIDE OF THE NIP. 